1. Field of the Invention
This invention relates to the purification of chloronitrosocyclohexane dimer (CNCD) which in its as produced relatively crude state must be freed of various impurities if it is to be useful in various applications, such as, for example, as an intermediate in the manufacture of L-lysine. The lysine process involves the subsequent steps of amination of the CNCD to aminocyclohexanone oxime (ACO); the Beckmann rearrangement of the ACO to produce .alpha.-amino-.gamma.-caprolactam (ACL); the neutralization, isolation, resolution and racemization of the ACL to yield L-.alpha.-amino-.gamma.-caprolactam hydrochloride (L-ACL.HCl) followed by hydrolysis of the L-ACL.HCl to yield L-lysine.HCl in high purity.
2. Description of the Prior Art
The reaction of nitrosyl chloride with olefins has been studied intensively and, for example, has played a major role in the structure determination and identification of terpenes. Depending on experimental conditions and olefin structures, the reaction leads to 2-chloro-1-nitrosoalkane dimers, chloro-oximes, chloronitro compounds, dichloro compounds, dichloro-nitroso compounds and nitro-nitroso compounds.
In particular, in the course of manufacture of L-lysine, 2-chloro-1-nitroso-cyclohexane dimer (CNCD) is derived from cyclohexane. The preparation of CNCD has long been known. U.S. Pat. No. 2,485,180, for example, describes the synthesis of CNCD and terpene derived dimers by using liquid SO.sub.2 as the reaction solvent at preferred temperatures between -40.degree. and -60.degree.C. The chloro-nitroso dimer obtained from liquid SO.sub.2 solvent appears to be the result of a trans addition of NOCl to the double bond and the structure has accordingly been assigned trans -2,2'-dichloro-trans-azodioxycyclohexene. The production of the dimer has in general been accompanied by substantial amounts of impurity which has interfered with or at least presented practical difficulties with the subsequent use of the intermediate to produce a product, i.e. lysine requiring high standards of purity.